A NASA probe has spotted hundreds of small surface fractures near Mars' equator that may have acted as underground natural plumbing to channel ground water billions of years ago.

Geologists compare the fractures in the sandstone rock deposits on Mars to features called deformation bands on Earth, which can arise from the influence of ground water in the underground bedrock. The bands and faults have strong influences on groundwater movement on Earth, and seem to have played the same role on Mars. Other research has examined how surface water from rain or snow shaped the planet surface, but many agree that groundwater has an equally important influence.

"Groundwater often flows along fractures such as these, and knowing that these are deformation bands helps us understand how the underground plumbing may have worked within these layered deposits," said Chris Okubo, a geologist with the U.S. Geological Survey in Flagstaff, Ariz., who headed up a new study of the Martian fractures.

The observations, made by NASA's Mars Reconnaissance Orbiter, showed how water has already changed the color and texture of the Martian sandstone along the fractures. Okubo's report on the finding is detailed online this month in the Geological Society of America Bulletin.

"This study provides a picture of not just surface water erosion, but true groundwater effects widely distributed over the planet," said Suzanne Smrekar, deputy project scientist for the MRO mission at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who was not part of the study. "Groundwater movement has important implications for how the temperature and chemistry of the crust have changed over time, which in turn affects the potential for habitats for past life."

Okubo and his study co-authors looked to similar patterns in Utah sandstones on Earth, where fractures are typically a few yards (meters) wide and up to several miles long. Such cracks reveal themselves as the rock layers on top erode away.

MRO found similar fractures in a 43-mile-wide (70-kilometer-wide) crater that sits just slightly north of the Red Planet's equator. Discovery of the deformation bands within the crater prompted scientists to name it after the late Charles Capen, an astronomer who worked at observatories in Southern California and Flagstaff, Ariz.